Commercial buildings frequently have what are referred to as flat roofs. Such flat roofs must have a slight pitch in order to direct water to a drain. The drain may be at the edge of the building or a corner, or can be in a central portion of the roof in which case there must be a depressed area or sump where the drain is located to encourage water to flow towards the drain. Typically, foam insulation is used to provide the slope. Panels of foam insulation can be formed with a thick edge and a thin edge. These are generally 4×8 sheets of polyisocyanurate foam. These can be purchased having the desired slope. The sump is then formed by cutting individual sheets at the job site to desired size and position around the drain. The waterproof membrane is applied over this and flashing provided at the drain to insure there is no leakage.
This is relatively time consuming. It requires a relatively skilled worker to cut the foam and it also causes a lot of waste at the job site. This makes it difficult to recycle wasted material or to use it for any other purpose. These sumps can be relatively large, i.e., generally 8×8 sections. Typically, roofing materials are 4×8 in size for shipping purposes.